The mechanism of synthesis of proteins is studied from the following viewpoint: It is assumed that the mechanism today represents an evolutionary elaboration about a simple archetype mechanism, the latter comprising tRNAs (or their predecessors) and probably the 5S RNA. In this view, the ribosome itself becomes the source, not of function per se, but of specificity. The present work attempts to elucidate the critical areas in the ribosomal RNAs through comparative and functional characterization, and a characterization of ribosomal protein - RNA interaction (binding sites).